Power management in electronic devices is becoming increasingly important as greater reliance is placed on battery power, e.g., for portable computers, personal data assistants (PDAs), tablet computers, cellular phones, pagers, and wireless computer peripherals. The components of such devices are becoming increasingly power hungry, and the demand for longer intervals between battery replacement or recharging has increased. Such devices are often turned on for ready usability but left idle for significant periods of time. This presents an opportunity to reduce depletion of battery power through the use of reduced power modes.
Recently, wireless peripheral devices intended for use with a host computer have been introduced. In particular, cursor control (pointing) devices such as a computer mouse and trackball device have been made wireless by inclusion of a battery power source within the device and the provision of a wireless data link, e.g., an infrared or RF transmitter/receiver pair. Without effective power management, continuous operation of such wireless peripherals will rapidly deplete the limited battery power of the device, thus requiring frequent battery replacement or recharging.
In another line of technological development, cursor control devices utilizing optical surface tracking systems have been introduced and are increasingly being used in lieu of devices relying on conventional opto-electric encoder wheel arrangements. Optical tracking can provide more reliable and accurate tracking by eliminating moving parts (e.g., a ball and associated encoder wheels), which are prone to malfunction from the pick-up of dirt, oils, etc. from the tracked support surface and/or a user's hand. On the other hand, optical tracking requires considerably more power for driving the circuitry used to illuminate a trackable surface and to receive and process light (image information) reflected from the trackable surface. Exemplary optical tracking systems, and associated signal processing techniques, are disclosed in commonly owned U.S. Pat. No. 6,172,354 (Adan et al.) and copending application Ser. No. 09/692,120, filed Oct. 19, 2000, and Ser. No. 09/273,899, filed Mar. 22, 1999, each of which is hereby incorporated by reference in its entirety.
Heretofore, limited use of optical tracking systems has been made in wireless cursor control devices, due to the relatively large power requirements of both the optical tracking system and the wireless data transmitter. In one recent offering, the Logitech Cordless Mouseman® Optical, multiple sleep and awake modes are utilized to increase battery life. Switching from a full run mode through a succession of reduced power modes is carried out based upon durations of user inactivity. Whenever the user moves the mouse or clicks a mouse button, the mouse returns to the full run mode.
Various types of user proximity detectors are known, and used in power management systems and myriad other applications. For example, Tournai U.S. Pat. No. 5,408,668 describes a processor based control system for connecting and disconnecting a computer peripheral device (e.g., a display monitor or printer) to a power source. The control is based upon input activity signals received from an input source such as a keyboard, mouse, printer or an occupancy sensor.
Mese et al. U.S. Pat. No. 5,396,443 describes power saving control arrangements for information processing apparatus. More specifically, the Mese et al. '443 patent describes various systems for (1) detecting the approach (or contact) of a user associated medium to (or with) the apparatus; (2) placing a controlled object of the apparatus in a non-power saving state when such contact or approach is detected; and (3) placing the controlled object in a power saving state when the presence of the user associated medium (i.e., a stylus pen or part of a user's body) is not detected for a predetermined period of time.
The '443 patent describes various types of approach/contact sensors. Among these, various “tablet” type sensor systems are described, including electromagnetic, capacitance, and electrostatic coupling tablets. In one embodiment, a contact or approach detecting tablet, and a flat display panel, may be integrally formed with a housing of the information processing apparatus.
Philipp U.S. Pat. No. 5,730,165 describes a capacitive field detector used to provide on-off control of a water fountain or wash basin faucet, based upon a detected approach or presence of a user.
In one embodiment of the Philipp '165 patent, a voltage-limited current source feeds a charging current to a plate. At the end of a charging interval, a discharge switch controlled by a microprocessor closes briefly to discharge the sensing plate into a charge detector, e.g., a charge detecting capacitor. The amount of charge so transferred is representative of the capacitance of the sensing plate. The charge-discharge process can be repeated numerous times, in which case the charge measurement means aggregates the charge from the plate over several operating cycles. After a predetermined number of cycles of charge and discharge, the charge detector is examined for total final charge, by an A/D converter, and as a result the controller may generate an output control signal on an output line, which may be used to cause a faucet to open. After each reading, the controller resets the charge detector to allow it to accumulate a fresh set of charges from the plate. Alternatively, the controller can take a reading after each individual cycle of the discharging switch, and then integrate (or otherwise filter) the readings over a number of cycles prior to making a logical decision resulting in a control output.
Sellers U.S. Pat. No. 5,669,004 describes a system for reducing power usage in a personal computer. More specifically, a power control circuit is disclosed for powering down portions of a personal computer in response to user inactivity, and for delivering full power to these portions once user activity is detected via one or more sensors. The components to which power is reduced (or removed) are components, which can respond almost immediately to being turned on. On the other hand, components which require a period of time to come up to full operation (e.g., disk drive motors, monitor, main processor) are driven to full power. In the primary embodiment that is disclosed, the sensor is a piezoelectric sensor fitted into a keyboard. Sellers discloses that sensors may be positioned at other locations on the computer (a monitor, mouse, trackball, touch pad or touch screen) and that various other kinds of sensors (capacity, stress, temperature, light) could be used instead of piezoelectric sensors.
Commonly owned copending U.S. patent application Ser. No. 09/948,099 (hereby incorporated by reference), filed Sep. 7, 2001 and published under No. 20020035701 on Mar. 21, 2002, discloses capacitive sensing and data input device power management systems and methods. In the disclosed embodiments, capacitive proximity sensing is carried out by detecting a relative change in the capacitance of a “scoop” capacitor formed by a conductor and surrounding ground plane. The conductor may be a plate provided in the form of an adhesive label printed with conductive ink. Charge is transferred between the scoop capacitor and a relatively large “bucket capacitor,” and a voltage of the bucket capacitor is applied to an input threshold switch. A state transition from low to high (or high to low) of the input threshold is detected, and a value indicative of the number of cycles of charge transfer required to reach the state transition is determined. The presence or absence of an object or body portion in close proximity to or in contact with a device can be determined by comparing the value with a predetermined threshold. The predetermined threshold can be adjusted to take into account environmentally induced changes in capacitance of the scoop capacitor.
With the above system implemented, e.g., in a wireless optical mouse or handheld digitizing pen, a change in environmental capacitance caused by the proximity of a user's hand is detected so that power can be saved by turning “off” the high current optical (or other type of) tracking system when the mouse/pen is not in use. The determination of this condition requires periodic sequences of microprocessor operation, causing increased current draw during the detection interval. This interval remains relatively long, because each time the touch system is operated a count is generated as the “bucket” capacitor is charged from 0 Volts up to the arbitrary threshold determined by the internal comparator.
The typical mouse user wants no sign of lag or delay in mouse response. Users are generally sensitive to motion down to approximately 0.01 ips and can move a mouse up to approximately 25 ips. Optical tracking affords a level of responsiveness commensurate with user sensitivities. When capacitive sensing techniques, e.g., as described in application Ser. No. 09/948,099, are used to detect operator interaction, however, aggressive users, e.g., gamers utilizing a mouse or other gaming peripheral (e.g., a gamepad), may move fast enough to notice a lack of responsiveness, due to the interval delay required to successfully detect a hand actuation. Sampling at a higher rate can alleviate perceived deficiencies in responsiveness, but increased sampling adversely affects battery life.
The use of battery power for optical tracking in computer mice and other data input devices presents a significant challenge from a power management perspective. Known optical tracking engines requires substantial current from the limited battery source. Additionally, the time and energy that it takes to detect hand presence limit the periodicity (frequency) with which detection sampling might take place. A faster, more power efficient, detection system would advantageously allow increased periodicity of the sampling and thus a more responsive detection of hand presence, and/or increased battery life.